The Big Bend area, also known as the Trans Pecos, occupies the extreme western part of the state eastward to the Pecos River. This is a region of diverse habitats and vegetation, varying from desert valleys and plateaus to wooded mountain slopes. Elevations range from 1,850 feet to more than 8,749 feet at Guadalupe Peak. Even the
mountain ranges vary greatly in the environments they offer for plant and
animal life; some are characterized by volcanic rocks, others by limestone.

Over most of the area, average annual rainfall is less than
12 inches but varies greatly from year to year and from lower to higher
elevations. July and August are usually the higher rainfall months.

West Texas streams are part of a very fragile ecosystem, dependent upon a
scarce water supply, often fed by springs. As in other parts of the state,
these streams provide a variety of habitats, from shallow, swift-flowing areas
to deeper, slow-moving pools supporting a variety of fish, reptiles, amphibians,
insets and mammals. Because water is scarce here, the riparian areas (banks
of a river, stream or lake) team with wildlife.

Cienegas are small isolated spring-fed wetlands that occur in desert
areas of the Trans-Pecos. In some areas, mountain springs create small wetlands
in higher elevations. Cienegas and mountain springs provide enough water for
plants and animals that don’t normally survive in the desert, giving
west Texas a much greater variety of species than most people would think.

Human activity can affect these streams and cienegas. Overuse of water from
aquifers can lower the water table to the point that springs stop flowing and
springs dry up. Groundwater can carry pollutants to these streams if care is
not taken to contain or dispose of of pollutants properly. The type of vegetation
allowed to grow along stream banks can affect the amount of available water
(a single salt cedar can draw 30 gallons of water each day). Destroying all
vegetation or disturbing stream beds will reduce cover and food for fish.

Mountain outwash materials have formed the soils of the Trans Pecos. Surface
textures and profile characteristics are varied, however. Due to the diversity
of soils and elevations, many vegetation types exist in the region. The principal
plant communities are creosote-tarbush desert scrub, desert grassland, yucca
and juniper savannahs, and montane forests of pinon pine and oak.

The various subregions reflect the diversity of the Trans Pecos. The Sand
Hills area consists of shin oak and mesquite on wind-blown dunes. Flat-topped
mesas and plateaus are intersected by steep-walled canyons and dry washes that
comprise the Stockton Plateau. Soils with high salt content and gypsum dunes
are typical of the Salt Basin area. The Desert Scrub subregion is an area of
low rainfall and rapid drainage. Creosotebush flats with yucca, lechuguilla,
and various small-leafed plants are common. The Desert Grassland area occurs
in the central part of the region and is characterized by deeper soils with
high clay content. Finally, the Mountain Ranges have higher rainfall and woody
vegetation such as junipers, oaks, pinon pine, ponderosa pine, and Douglas
fir.

Ranching is the primary industry in the Trans Pecos region.

Water Supply and Demand

Supply

Major River: Rio GrandeMajor Aquifer: Hueco-Mesilla Bolson

Use & Demand

60% demand met through surface water.

75% demand is for irrigation, 22% for municipal needs.

By 2050, the population of the area is expected to double. The demand for
water is expected to change to 50% for irrigation, and 44% for municipal
needs. (Source: Texas Center for Policy Studies. Texas Environmental Almanac
(Austin: U.T. Press, 2002), 22.)